Kathy- the beauty of the inquiry method of learning science is that the teachers is NOT the fount of all knowledge. You can put on an air of slight uncertainty in these activities as you encourage the children to make predictions using:
I think that XXX will happen if we do YY because…
You can help them phrase their thinking, and challenge if they are predicting one thing that is totally at odds with why they think it will happen, but you (and they) don’t need to know the “Right” answer before you start.
So, for forces, a child might say:
I think a big toy car won’t go as far when it goes down a ramp, because it takes more push to throw a heavy ball… and then you test this.